Planar transformer winding

ABSTRACT

The invention concerns a planar transformer winding comprising primary and secondary coils with wire turns produced in the form of strip conductors formed on the surfaces of an insulting base and electrically connected with one another by means of conducting holes bored in the insulating base. The primary and secondary winding portions borne by one common surface of the insulating base are joined together by winding, along two distinct overlapping zones, spiral in shape, one of the zones joining side by side turns or portions of turns of the primary coil and the other zone joining together the turns or portions or turns of the secondary coil. Such an arrangement enables to obtain primary and secondary coils with a different number of turns on one single insulating base with two surfaces.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of priority under 35 U.S.C. § 119 toFrench Application Serial No. 97/16347, filed on Dec. 23, 1997 andclaims priority under 35 U.S.C. § 120 to Patent Cooperation TreatyApplication Serial No. PCT/FR98/02853, filed on Dec. 23, 1998; theentire contents of which are incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a coil for planar transformercomprising at least one primary winding and at least one secondarywinding, and more particularly such a coil of the type whose primary andsecondary windings comprise turns made in the form of conductive tracksformed on the faces of a plane insulating support or of several stackedplane insulating supports connected together, as need be, by conductiveholes passing through the plane insulating supports.

2. Discussion of the Background

In planar technology, a transformer winding, which is either primary orsecondary, consists of at least two portions of conductive tracks madeon different faces of one or several stacked plane insulating supportsin such a way as to be able to exhibit connection terminals arranged onthe periphery of the transformer, this being so as to ease electricalconnecting of the transformer. The portions of conductive tracks of oneand the same winding follow similarly directed spirals and are connectedtogether electrically so as to ensure the continuity of the winding, bythe inside ends of their spirals and, as need be, by certain of theoutside ends of their spirals by means of conductive holes passingthrough the insulating support or supports.

According to current practice, the conductive tracks of the primary andsecondary windings of a transformer are nested on the plane insulatingsupports so that there is an alternation of primary and secondary turnson any one of the plane insulating supports, on moving from the outsidetowards the centre of a transformer.

Although generally proving satisfactory, this solution has certaindrawbacks.

Firstly, when one wishes to have different numbers of loops for theprimary and for the secondary of a planar transformer, this beingrelatively frequent, it is necessary firstly to make, on one or severalstacked plane insulating supports, primary and secondary windings withthe same number of loops corresponding to the smallest of the numbers ofloops required. Then to terminate the winding having the largest numberof loops with complementary turns traced on one or several other planeinsulating supports. This may lead to the use of a high number ofstacked plane insulating supports whereas it is important to reduce thenumber of stacked plane insulating supports as far as possible for easeof construction.

Moreover, since the turns of the primary and secondary windings arealternated on the surface of the plane insulating supports, it isnecessary to provide therebetween a spacing making it possible to ensurethe desired electrical insulation between the primary and secondary ofthe transformer. Since the constraints of electrical insulation betweenprimary and secondary of a transformer are often sizeable, thisgenerally results in a non negligible spacing between each of theprimary and secondary turns traced alternately on the surface of one andthe same plane insulating support. This inter-turn spacing reduces thedensity of the turns, hence the number of turns which can be housed on agiven surface of plane insulating support. Apart from the fact that itlimits the possibilities for diminishing the bulkiness of thetransformer, it reduces the magnetic coupling thereby causing anincrease in the magnetic leakages. This results in a transformer whichis less effective than one might hope for, especially as regardsefficiency.

SUMMARY OF THE INVENTION

The present invention aims to alleviate these drawbacks.

To this end, the subject of the invention is a coil for planartransformer comprising at least one primary winding and at least onesecondary winding with turns made in the form of conductive tracksformed on the faces of an insulating support and connected together bymeans of conductive holes drilled in the insulating support,characterized in that the portions of the primary and secondary windingscarried by one and the same face of the insulating support are groupedtogether on a per-winding basis, according to two separate nested zones,of spiral shape, one of the zones grouping together, side by side, turnsor portions of turns of the primary winding and the other zone groupingtogether, side by side, turns or portions of turns of the secondarywinding.

Such a structure, although complex from the geometrical point of view,does not exhibit any more technological difficulties to be constructedthan that of the prior art.

On the other hand, it makes it possible to construct on the two faces ofone and the same plane insulating support, an entire coil, comprisingprimary and secondary windings having different numbers of loops. Atransformer made according to the invention can therefore comprise fewerlayers of supports, even if it generally has several of them, andconsequently be less expensive and less voluminous.

It furthermore makes it possible to pack the turns closer togetherwithin one and the same zone on a plane insulating support face sincethey belong to one and the same primary or secondary winding for whichthe requirements of inter-turn insulation are always lesser than therequirements of insulation between primary and secondary windings. Thismakes it possible to improve the compactness of the transformer andhence to limit its magnetic losses.

In a particular embodiment of the invention, each winding portion formsa turn which extends over approximately 360°.

This layout has the advantage of being simple, since it leads easily tocomplete turns when two portions of winding are connected togetherelectrically by a conductive hole joining the inside ends of theirturns.

Also in a particular embodiment, one at least of the windings is formedon each face of the support of a plurality of winding portions joinedsuccessively from one face to the other of the support, in series byconductive holes.

It will be seen hereinbelow that this layout, which is alsogeometrically complex, makes it possible to arrange for numerous turnsof the primary winding (respectively secondary winding) to be oppositethe secondary winding (respectively primary winding).

Advantageously, the turns of each winding have shapes such that theycreate superposed indentations through which the conductive holes of theother winding pass.

Such an arrangement allows the best possible superposition of theprimary and secondary windings, and it thus makes it possible to improvethe magnetic performance of the transformer.

The subject of the present invention is also a multiple coil for planartransformer, comprising a plurality of coils as described hereinabovearranged one above another on a plurality of assembled supports, theprimary and secondary windings respectively of the said coils beingelectrically linked to one another.

The said windings may then be linked either in series, or in parallel.

Provision may furthermore be made for several primaries and/or severalsecondaries.

BRIEF DESCRIPTION OF THE DRAWINGS

A particular embodiment of the invention will now be described by way ofnon-limiting example, with reference to the appended diagrammaticdrawings in which:

FIG. 1 is a perspective view of a transformer coil according to theinvention;

FIGS. 2 and 3 illustrate, respectively in perspective and in plan view,a portion of winding according to the invention;

FIG. 4 illustrates another embodiment of a coil according to theinvention, a single winding being represented; and

FIG. 5 is a perspective view of another embodiment of the invention.

FIG. 6 is another view of the embodiment of the invention shown in FIG.5, the insulating support being represented.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

It will be noted that the insulating supports onto which the conductivetracks whose layout forms the subject of the present invention areperfectly known in themselves, as is the manner of superposing them, andof forming conductive tracks on their faces, for example by printingwith conductive ink or affixing a metal foil.

FIG. 1 shows two identical elementary coils 1 and 2 joined together as amultiple coil. Each of the coils is formed of a primary winding and of asecondary winding, nested together, each being made partially on each ofthe faces, upper and lower, of the support on which this elementary coilis formed.

The primary winding, for example, is formed of a first conductive span 3extending over approximately 360° around the axis of the coil, so as toform a first turn on the upper face of the support, and of a secondconductive span 4 also extending over approximately 360° around the axisof the coil, so as to form a second turn on the lower face of thesupport. In the same way, the secondary winding is formed of a firstconductive span 5 extending over approximately 360° around the axis ofthe coil, so as to form a first turn on the upper face of the support,and of a second conductive span 6 also extending over approximately 360°around the axis of the coil, so as to form a second turn on the lowerface of the support.

The various aforesaid spans, and hence the turns which result therefrom,are not circular but substantially helical, so that the first few turnsof each winding are nested on the upper face of the support, as are thesecond few turns on its lower face. In the present case or [sic] eachwinding comprises just one turn per face, this signifies that each turnof each winding passes between the ends of the turn, formed on the sameface of the support, of the other winding.

Moreover, each turn possesses a free end, the connection of which willbe described hereinbelow.

The other end of each turn of each winding lies, on a face of thesupport, opposite the other end of the turn of the same winding, on theother face of the support. These opposed ends are linked by conductiveholes 7 (FIG. 2) so as to ensure the electrical continuity of eachwinding from one of its free ends to the other.

It will be observed, and more particularly in FIG. 3, that the turns ofeach winding have shapes such that they create superposed indentations8. The conductive holes of the other winding pass through theseindentations, thereby making it possible to ensure optimal overlappingof the primary and secondary windings, and hence good performance fromthe magnetic point of view.

The free ends of the primary winding are linked to two linkingconductors 9 and 10 (here, double) perpendicular to the plane of thesupport and arranged side by side. Likewise, the free ends of thesecondary winding are linked to two similar linking conductors 11 and 12(of which one, here, is double). The linking conductors of the primaryand of the secondary are made in a known manner in the form ofconductive holes, when assembling the superposed supports.

The primary windings on the one hand, and the secondary windings on theother hand, of the coils 1 and 2 are here connected in parallel. FIG. 4shows however a multiple winding, primary or secondary, where threeelementary windings are connected in series with four conductive holes13 a-13 d. The layout of FIG. 4 does not differ otherwise from that ofFIG. 1 and will therefore not be described in greater detail.

It will have been appreciated that all the conductive spans representedhitherto in the drawings are split into two. This constitutes a knownarrangement related to the fact that the current is not uniformlydistributed over a given conductor on proceeding from the axis of theturn towards the outside. Each winding is therefore divided into twoconductors, each of these conductors passing to the inside on one of thefaces of the support and to the outside on the other face, therebymaking it possible to optimize the alternate resistances by forcing thesame current through the two branches.

Reference will now be made to FIGS. 5 and 6 (in which only one of thewindings is split into two as described in the above paragraph).Regarding FIG. 6, an insulating support 24 is shown. The insulatingsupport has first and second opposing faces on which the primary andsecondary windings are provided as described below. Regarding FIG. 5,the primary winding (for example) 20 and the connections of the windingsto the conductive holes 21 a-21 d are identical to those of FIG. 1Hence, only the secondary windings will be described.

The latter is formed of six helical spans each extending oversubstantially 360°, thus forming six turns, three on one face of thesupport and three on the other face. The first turn 22 a extends overthe upper face of the support from the conductive hole 21 c, on theoutside of the coil, to the inside of the coil. The winding thencontinues through a conductive hole 23 a where it passes through thesupport. The second turn 22 b therefore extends over the lower face ofthe support, from the conductive hole 23 a up to another conductive hole23 b, in proximity to the conductive hole 21 c. The third turn 22 cagain extends over the upper face, on the inside of the turn 22 a, fromthe conductive hole 23 b up to the conductive hole 23 c in proximity tothe conductive hole 23 a. The winding thus continues in series via theturn 22 d, the conductive hole 23 d, the turn 22 e, the conductive hole23 e, and the turn 22 f, which is connected to the conductive hole 21 d.

It is observed that the three turns 22 a, 22 c and 22 e of the secondarywinding 22 which are carried by the upper face of the support, arearranged side by side in one and the same zone reserved so to speak forthe secondary winding 22. This spiral-shaped zone is nested with anotherlikewise spiral-shaped zone which is itself reserved for the split turn20 b of the primary winding 20. This same arrangement of the turns intwo zones in the form of nested spirals, one reserved for the turns ofthe primary winding and the other for the turns of the secondarywinding, is found also on the other face of the support. Thisarrangement makes it possible, as has just been seen, to make primaryand secondary windings with different numbers of turns, here a primarywinding with a turn split into two and a secondary winding with sixsingle turns, while employing only one support with two faces. It alsoallows better use of copper because the insulation distances to becomplied with within each zone are lesser since only inter-turninsulation within one and the same winding is involved.

The coil just described in relation to FIG. 5 can obviously beassociated with others in parallel or in series, as in FIGS. 1 or 4respectively.

What is claimed is:
 1. A coil for a planar transformer comprising: aninsulating support having first and second opposing faces; a firstprimary winding portion provided on the first face of the insulatingsupport and including a plurality of turns formed of conductive tracks;a second primary winding portion provided on the second face of theinsulating support and including a plurality of turns formed ofconductive tracks; a first secondary winding portion provided on thefirst face of the insulating support and including a plurality of turnsformed of conductive tracks; a second secondary winding portion providedon the second face of the insulating support and including a pluralityof turns formed of conductive tracks; and at least a first linkingconductor configured to connect the first primary winding portion to thesecond primary winding portion and at least a second linking conductorconfigured to connect the first secondary winding portion to the secondsecondary winding portion through the insulating support; wherein theturns of the first primary winding portion are grouped together side byside around or inside the turns of the first secondary winding portionswhich are grouped together side by side on the first face of theinsulating support and the turns of the second primary winding portionare grouped together side by side around the turns of the secondsecondary winding portion which are grouped together side by side on thesecond face of the insulating support.
 2. Coil according to claim 1,characterized in that each winding portion carried by a face of theinsulating support forms a turn which extends over approximately 360°.3. Coil according to claim 1, characterized in that the turns of eachwinding are shaped such that they create superposed indentations throughwhich the linking conductors pass.
 4. Multiple coil for planartransformer, characterized in that it comprises a plurality of coilsaccording to claim 1, arranged one above another on a plurality ofassembled supports and connected together electrically, primary windingto primary winding and secondary winding to secondary winding by linkingconductors drilled through the assembled supports.
 5. Coil according toclaim 4, characterized in that the said windings are linked in series.6. Coil according to claim 4, characterized in that the said windingsare linked in parallel.
 7. Coil according to claim 4, characterized inthat it comprises at least several primary coils or several secondarycoils.
 8. Coil according to claim 1, wherein at least one turn of thefirst primary winding is connected in series with one of the turns ofthe second primary winding via one of the linking conductors and atleast one turn of the first secondary winding is connected in serieswith one of the turns of the second secondary winding via one of thelinking conductors.